An automatic geared transmission, as in the previously described art, is meant to be an automated shift transmission, an automatic clutch transmission, and a planetary automatic transmission. The term automatic geared transmission shall also include an automatic transmission where the transmission ratio can be continuously changed, but where a switch-over gear enables the transmission output drive shaft to reverse direction of rotation and in which, by means of suitably controlling transmission ratio change tools, it is possible to shift fixed pre-programmed transmission ratio steps.
An automatic geared transmission, designed as a lay shaft transmission, is usually linked to the engine with its input shaft via a single, controllable friction clutch, meaning an automatic engaging and disengaging such as, for instance, a passively engaging single disc or multiple disk dry clutch or an actively engaging multiple disk clutch, whereby the friction clutch performs the function of a starting element as well as the one of a shift clutch. In an automated double clutch transmission, constructed with two partial transmissions, with each having an input shaft, the two input shafts are each connectable with the engine via a controllable friction clutch. In contrast, a planetary automatic transmission is usually linked to the engine, by its input shaft, via a starting element which is designed as a hydro dynamic torque converter. But other combinations of automatic geared transmissions and starting elements are also possible, for instance a combination of an automatic geared transmission and an upstream hydro dynamic torque converter or a combination of a planetary automatic transmission with an upstream friction clutch.
In a motor vehicle where the drive train comprises such a combination of a geared transmission and a starting element, there is a general risk that when the engine is running with a disengaged drive train, meaning when the gearing is in a neutral position and/or the starting element is disengaged, that the motor vehicle starts rolling, unintended by the driver and similar to an engaged gear or along a down slope, which can create a dangerous situation for the passengers as well as for other users of the road.
It is therefore possible, for instance, that a motor vehicle which is equipped with an automatic geared transmission and a passively engaging friction clutch might start on its own with a running engine, a disengaged friction clutch and an engaged gear if there is a defect in the clutch control due to failure and the engaging friction clutch. To avoid this situation, a device and a method is proposed, in DE 199 26 697 A1, in which, when the motor vehicle has stopped and when the engine is running, the friction clutch is disengaged, and a gear is engaged, the geared transmission switches to its neutral position, meaning that the engaged gear becomes disengaged, when a not-ready to drive condition of the motor vehicle is recognized during a predetermined time interval.
A similar method, as in DE 102 58 834 A1, has in principle several other constructive drive trains so that for a standing motor vehicle, with a running engine, a disengaged friction clutch and an engaged gear, the geared transmission is shifted to neutral if over a predetermined time interval and open door of the motor vehicle is detected. Hereby, any unwanted starting of the motor vehicle, due to a failure in the clutch control or because of an unintended activation of a drive operating element, especially the throttle which will cause engagement of the friction clutch, can be avoided.
However, any unwanted rolling of the motor vehicle, due to a present uphill road slope or a downhill slope, respectively, hereby can not be prevented. In the case of a disengaged drive train and for a secure fixing of the motor vehicle, requires the driver to engage or sufficiently activate a parking brake. If the parking brake is not engaged or not sufficiently activated, for instance when the driver has underestimated the present slope and has, therefore, not sufficiently activated the parking brake, or when another passenger has unintentionally disengaged the parking brake, the motor vehicle can roll uncontrolled downhill. If the driver is in the driver seat in that situation and recognizes rolling, the uncontrolled rolling can be prevented by activating the brake or by engaging a gear, via the shift operating elements, and, if necessary, by activating the throttle. This, however, requires the driver to be present in his seat and the driver to have a high level of responsiveness, which cannot always be guaranteed.